cxl: Prevent adapter reset if an active context exists

This patch prevents resetting the cxl adapter via sysfs in presence of
one or more active cxl_context on it. This protects against an
unrecoverable error caused by PSL owning a dirty cache line even after
reset and host tries to touch the same cache line. In case a force reset
of the card is required irrespective of any active contexts, the int
value -1 can be stored in the 'reset' sysfs attribute of the card.

The patch introduces a new atomic_t member named contexts_num inside
struct cxl that holds the number of active context attached to the card
, which is checked against '0' before proceeding with the reset. To
prevent against a race condition where a context is activated just after
reset check is performed, the contexts_num is atomically set to '-1'
after reset-check to indicate that no more contexts can be activated on
the card anymore.

Before activating a context we atomically test if contexts_num is
non-negative and if so, increment its value by one. In case the value of
contexts_num is negative then it indicates that the card is about to be
reset and context activation is error-ed out at that point.

Fixes: 62fa19d4b4 ("cxl: Add ability to reset the card")
Cc: stable@vger.kernel.org # v4.0+
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Vaibhav Jain 2016-10-14 15:08:36 +05:30 committed by Michael Ellerman
parent 65bc3ece84
commit 70b565bbdb
9 changed files with 121 additions and 7 deletions

View file

@ -220,8 +220,11 @@ What: /sys/class/cxl/<card>/reset
Date: October 2014
Contact: linuxppc-dev@lists.ozlabs.org
Description: write only
Writing 1 will issue a PERST to card which may cause the card
to reload the FPGA depending on load_image_on_perst.
Writing 1 will issue a PERST to card provided there are no
contexts active on any one of the card AFUs. This may cause
the card to reload the FPGA depending on load_image_on_perst.
Writing -1 will do a force PERST irrespective of any active
contexts on the card AFUs.
Users: https://github.com/ibm-capi/libcxl
What: /sys/class/cxl/<card>/perst_reloads_same_image (not in a guest)

View file

@ -229,6 +229,14 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed,
if (ctx->status == STARTED)
goto out; /* already started */
/*
* Increment the mapped context count for adapter. This also checks
* if adapter_context_lock is taken.
*/
rc = cxl_adapter_context_get(ctx->afu->adapter);
if (rc)
goto out;
if (task) {
ctx->pid = get_task_pid(task, PIDTYPE_PID);
ctx->glpid = get_task_pid(task->group_leader, PIDTYPE_PID);
@ -240,6 +248,7 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed,
if ((rc = cxl_ops->attach_process(ctx, kernel, wed, 0))) {
put_pid(ctx->pid);
cxl_adapter_context_put(ctx->afu->adapter);
cxl_ctx_put();
goto out;
}

View file

@ -238,6 +238,9 @@ int __detach_context(struct cxl_context *ctx)
put_pid(ctx->glpid);
cxl_ctx_put();
/* Decrease the attached context count on the adapter */
cxl_adapter_context_put(ctx->afu->adapter);
return 0;
}

View file

@ -618,6 +618,14 @@ struct cxl {
bool perst_select_user;
bool perst_same_image;
bool psl_timebase_synced;
/*
* number of contexts mapped on to this card. Possible values are:
* >0: Number of contexts mapped and new one can be mapped.
* 0: No active contexts and new ones can be mapped.
* -1: No contexts mapped and new ones cannot be mapped.
*/
atomic_t contexts_num;
};
int cxl_pci_alloc_one_irq(struct cxl *adapter);
@ -944,4 +952,20 @@ bool cxl_pci_is_vphb_device(struct pci_dev *dev);
/* decode AFU error bits in the PSL register PSL_SERR_An */
void cxl_afu_decode_psl_serr(struct cxl_afu *afu, u64 serr);
/*
* Increments the number of attached contexts on an adapter.
* In case an adapter_context_lock is taken the return -EBUSY.
*/
int cxl_adapter_context_get(struct cxl *adapter);
/* Decrements the number of attached contexts on an adapter */
void cxl_adapter_context_put(struct cxl *adapter);
/* If no active contexts then prevents contexts from being attached */
int cxl_adapter_context_lock(struct cxl *adapter);
/* Unlock the contexts-lock if taken. Warn and force unlock otherwise */
void cxl_adapter_context_unlock(struct cxl *adapter);
#endif

View file

@ -205,11 +205,22 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
ctx->pid = get_task_pid(current, PIDTYPE_PID);
ctx->glpid = get_task_pid(current->group_leader, PIDTYPE_PID);
/*
* Increment the mapped context count for adapter. This also checks
* if adapter_context_lock is taken.
*/
rc = cxl_adapter_context_get(ctx->afu->adapter);
if (rc) {
afu_release_irqs(ctx, ctx);
goto out;
}
trace_cxl_attach(ctx, work.work_element_descriptor, work.num_interrupts, amr);
if ((rc = cxl_ops->attach_process(ctx, false, work.work_element_descriptor,
amr))) {
afu_release_irqs(ctx, ctx);
cxl_adapter_context_put(ctx->afu->adapter);
goto out;
}

View file

@ -1152,6 +1152,9 @@ struct cxl *cxl_guest_init_adapter(struct device_node *np, struct platform_devic
if ((rc = cxl_sysfs_adapter_add(adapter)))
goto err_put1;
/* release the context lock as the adapter is configured */
cxl_adapter_context_unlock(adapter);
return adapter;
err_put1:

View file

@ -243,8 +243,10 @@ struct cxl *cxl_alloc_adapter(void)
if (dev_set_name(&adapter->dev, "card%i", adapter->adapter_num))
goto err2;
return adapter;
/* start with context lock taken */
atomic_set(&adapter->contexts_num, -1);
return adapter;
err2:
cxl_remove_adapter_nr(adapter);
err1:
@ -286,6 +288,44 @@ int cxl_afu_select_best_mode(struct cxl_afu *afu)
return 0;
}
int cxl_adapter_context_get(struct cxl *adapter)
{
int rc;
rc = atomic_inc_unless_negative(&adapter->contexts_num);
return rc >= 0 ? 0 : -EBUSY;
}
void cxl_adapter_context_put(struct cxl *adapter)
{
atomic_dec_if_positive(&adapter->contexts_num);
}
int cxl_adapter_context_lock(struct cxl *adapter)
{
int rc;
/* no active contexts -> contexts_num == 0 */
rc = atomic_cmpxchg(&adapter->contexts_num, 0, -1);
return rc ? -EBUSY : 0;
}
void cxl_adapter_context_unlock(struct cxl *adapter)
{
int val = atomic_cmpxchg(&adapter->contexts_num, -1, 0);
/*
* contexts lock taken -> contexts_num == -1
* If not true then show a warning and force reset the lock.
* This will happen when context_unlock was requested without
* doing a context_lock.
*/
if (val != -1) {
atomic_set(&adapter->contexts_num, 0);
WARN(1, "Adapter context unlocked with %d active contexts",
val);
}
}
static int __init init_cxl(void)
{
int rc = 0;

View file

@ -1487,6 +1487,8 @@ static int cxl_configure_adapter(struct cxl *adapter, struct pci_dev *dev)
if ((rc = cxl_native_register_psl_err_irq(adapter)))
goto err;
/* Release the context lock as adapter is configured */
cxl_adapter_context_unlock(adapter);
return 0;
err:

View file

@ -75,12 +75,31 @@ static ssize_t reset_adapter_store(struct device *device,
int val;
rc = sscanf(buf, "%i", &val);
if ((rc != 1) || (val != 1))
if ((rc != 1) || (val != 1 && val != -1))
return -EINVAL;
if ((rc = cxl_ops->adapter_reset(adapter)))
return rc;
return count;
/*
* See if we can lock the context mapping that's only allowed
* when there are no contexts attached to the adapter. Once
* taken this will also prevent any context from getting activated.
*/
if (val == 1) {
rc = cxl_adapter_context_lock(adapter);
if (rc)
goto out;
rc = cxl_ops->adapter_reset(adapter);
/* In case reset failed release context lock */
if (rc)
cxl_adapter_context_unlock(adapter);
} else if (val == -1) {
/* Perform a forced adapter reset */
rc = cxl_ops->adapter_reset(adapter);
}
out:
return rc ? rc : count;
}
static ssize_t load_image_on_perst_show(struct device *device,